Are You Paying to Remove Excess Water with Your Sludge?
No matter the type of wastewater facility you manage, your primary job is to remove contaminants from the water that cannot go to the local municipality, watershed or environment. However, when contaminants are collected, excess water often remains trapped in the waste. That extra water increases your disposal costs, whether it’s through higher hauling fees or additional processing to prepare the waste for reuse.
Dewatering sludge produced by your DAF (Dissolved Air Flotation system), clarifier, or lagoon can significantly reduce hauling expenses and, in some cases, even allow you to sell your waste to other companies. If you aren’t already dewatering, consider these mechanical techniques. The goal is simple: remove as much water as possible before the sludge leaves your facility.
Mechanical Dewatering Technologies
1. Centrifuge
Centrifuges work by spinning sludge at high speeds, using centrifugal force to separate solids from liquids. Solids are pushed to the outer edge of the bowl, while water collects at the center for removal.
Advantages:
- High Throughput: Can process large volumes of sludge quickly.
- High Solids Concentration: The centrifugal force allows for high levels of solids capture and relatively low residual moisture in the sludge.
- Compact Design: Typically have a smaller footprint compared to other technologies, making them ideal for facilities with limited space.
Disadvantages:
- High Energy Consumption: Requires significant energy due to the high speeds involved.
- Noise and Vibration: Centrifuges can produce a considerable amount of noise and vibration, potentially necessitating additional soundproofing or vibration control measures.
- Maintenance-Intensive: Have numerous moving parts, which are subject to wear and tear and require regular maintenance.
2. Screw Press
A screw press uses a narrowing cylindrical screw to gradually apply pressure, forcing water out through perforated screens.
Advantages:
- Low Energy Usage: Operate at lower speeds, consuming less energy than centrifuges.
- Low Maintenance: Fewer moving parts mean reduced maintenance requirements.
- Continuous Operation: Suitable for steady sludge processing.
Disadvantages:
- Lower Solids Capture Rate: Screw presses may produce a lower solids concentration compared to centrifuges, resulting in wetter sludge.
- Slower Throughput: The process is generally slower, limiting their suitability for facilities with large volumes of sludge.
- Potential for Clogging: Screw presses can be prone to clogging, particularly when processing sludge with high fibrous or sticky content.
3. Multi-Disc Screw Press
Multi-disc screw presses use rotating discs covered with filter cloths to separate solids from liquids. The design provides a large surface area for filtration while minimizing energy use.
Advantages:
- Low Energy Consumption: The slow-moving, gravity-assisted process uses minimal energy.
- Low Maintenance Requirements: With few moving parts, the system is less prone to mechanical failure.
- Compact Design and Space-Efficiency: Multi-disc filters are compact and can often be scaled to fit within existing infrastructure.
Disadvantages:
- Moderate Solids Capture Rate: Multi-disc filters may not achieve as high a solids concentration as centrifuges.
- Vulnerable to Variability in Sludge Consistency: The performance of multi-disc filters can be inconsistent with variable sludge characteristics.
- Lower Throughput: While efficient for small to medium facilities, multi-disc filters may not handle high sludge volumes as effectively as centrifuges.
4. Frame Filter Press
A frame filter press applies high-pressure filtration to separate solids from liquids. Sludge is pumped into filter chambers lined with cloth, where water is squeezed out.
Advantages:
- High Solids Capture: Produces a drier cake compared to other technologies.
- Customizable: Modular design allows scaling to match facility needs.
- Low Energy Use: Uses pressure rather than mechanical motion, conserving energy.
Disadvantages:
- Batch Process: Requires downtime for cleaning and resetting.
- Labor-Intensive: More manual intervention compared to continuous systems.
- Large Footprint: Occupies more space than centrifuges or screw presses.
The Role of Polymers in Dewatering
Polymers play a critical role in the dewatering process by enhancing solid-liquid separation. They encourage flocculation—forming larger flocs—which improves sludge dryness and reduces disposal costs. Flocculation decreases the likelihood of equipment blockages, particularly in screw presses and multi-disc filters.
However, not all polymers are created equal. From cationic to anionic polymers, they vary in molecular weight and charge. Choosing the right polymer for your process can be complex, but that’s where Watertech of America can help. Our team performs drainage studies and “flop” testing to identify the optimal solution for your system, ensuring efficiency and cost savings. If you have questions about dewatering options or better ways to manage your sludge, reach out for a site survey and one of our technical engineers will be in touch.
Jason Waack, Territory Manager, Watertech of America, Inc.
Jason has 19 years’ experience in the water treatment industry. He has been a Territory Manager with Watertech for 9 years, managing accounts in the central part of Wisconsin. Jason frequently leads educational training events and seminars to promote better water management and improve safety.